Shale gas refers to the natural gas accumulated in the dark mud shale or high-carbon mud shale and existing mainly in an absorbed or free form. Shale gas has the same physical and chemical properties as the conventional natural gas except that it adheres to and exists in the mud shale with extremely low permeability and porosity. The development depth range of shale gas is more than that of the coalbed gas, while its porosity, permeability and saturation are less than those of the coalbed gas. It thus becomes increasingly difficult to exploit shale gas to a great extent, and it is considered as non-conventional oil-gas resource by the industry.
As shale gas usually deposits in the compact rock stratum, it is considered to have high exploitation difficulty, low input-output ratio and high cost.
As shown in Neijiang Science Technology, Period 12, page 131, Table 3 (2010), for the shale gas exploitation in general, production enhancement measures and special well drilling methods need to be adopted because the shale gas is found in the shale fractures, micro-holes and stratum and such reservoir stratum typically has much lower permeability and higher gas flow resistance when compared with traditional natural gas formations.
As disclosed in Natural Gas Earth Science, Period 3, Volume 22, pages 511-516 (June, 2011), the main difference between shale gas exploitation and traditional natural gas exploitation is that in the shale gas exploitation process, horizontal well drilling and hydraulic fracturing methods are used in general. That is to say, on the basis of the provision of straight well, a horizontal well is provided as an auxiliary means to improve the collection rate. Furthermore, by combination with fracturing treatments, the permeability of the reservoir stratum can be further improved so that the gas in the stratum can flow into the well more easily.
However, the conventional shale gas operation method has the following disadvantages.
1. The operation cost is high. This is because in the multiple steps such as well drilling and fracturing, a diesel generator or an external power supply is needed as the power source for the equipment such as electric drilling machines and fracturing vehicles.
2. In general, a rigid round tank is used for storing water or for recovering liquids discharged from the well during the fracturing operation. During a fracturing operation, tens of rigid round tanks are needed for storing thousands of liters of water. Moreover, because of the large volume of the rigid tanks, they are not convenient to handle and require a large area for the well site. Also, the costs for transportation, leveling the well site, and the environmental recovery are high.
The shale gas operation method of the present disclosure addresses one or more of the problems set forth above.